Relaxation oscillation for interlaced scanning



April 4, 1939. K. SCHLESINGER 2,152,822 V RELAXATION OSCILLATION FOR INTERLACED SCANNING Filed Nov. 20, 1955 Jnrew/or:

Patented Apr. 4, 1939 UNITED STATES PATET OFFER RELAXATION OSCILLATION FOR INTER,-

LAOED SCANNING Steglitz, Germany Application November 20, 1935, Serial No. 50,738 In Germany November 23, 1934 3 Claims.

The present invention relates to a relaxation oscillation connection, more particularly for television receivers, which are constructed to receive a transmission from a television transmitter operating with interlaced scanning.

In the drawing Fig. 1 shows the relaxation oscillation system according to the invention.

Fig. 2 shows a diagram of the charging and discharging periods of a relaxation oscillation connection for interlaced scanning.

The relaxation apparatus operating with charging condenser, charging resistance and gasfilled glow discharge tube has proved to be extremely satisfactory upon the television reception of normal screen transmissions.

There exists, however, a certain difiiculty in the case of interlaced scanning at an even number of lines as it will be described.

In Fig. 1, 3 is a gasfilled discharge tube having anode 4, hot cathode 5 and control grid 6. The latter is, as well known, negatively biassed and is made positive by the synchronizing signals coming from the lead 8. The terminal M of the storage condenser I is connected to the anode 4 and via the charging resistance 2 to the positive terminal of a D. C. source whilst the second terminal 13 of the condenser is earthed. The frame deflecting plates of the cathode ray tube (not designated) are connected to the terminals of condenser I. In a television system working at an odd number of interlaced lines, as mostly used, the condenser I is connected in parallel to the anode and cathode of the tube 3 either directly or via a small resistance. The synchronizing signals are given at equal time intervals and the time curve of the deflecting voltage arising in this case is of regular saw-tooth form.

If, on the contrary, the number of lines per image is an even one, the synchronizing signals are given by the transmitter alternatively for the time of a line earlier and later. Fig. 2 shows a time graph 2| to 21 of the wanted deflections or deflecting voltages. The points 22 and 26 lie for the width of a line higher than point 24, point 23 as much higher than the points 2| and 25. The break-down of the voltage at the points 22 and 24 is obtained at a desired moment by the ignition of the tube caused by the synchronizing impulses. It is, however, not so easy to eifect that the beginning of the recharging of the condenser, i. e. the quenching of the tube, takes place at (e. g.) 25 and not at 25'. When the condenser l is connected to the tube 3 directly or via an 5 ohmic resistance, the discharge is strongly damped and the voltage at which the quenching occurs is independent of the maximum voltage 22 or 24 However, in order to obtain the correct position of the second group of lines, it is necessary to bring the beginning of the ascending defiection line at 25 a little lower, so that the distance 24-25 gets equal to the distance 22-23.

According to the invention this is obtained by inserting in the discharge connection a timing circuit consisting of a condenser l4 shunted by a resistance or self-induction Hi. This way the time between ignition and quenching is kept constant as wanted. Supposed a scanning at 2 x lines it has been found that the capacity l4 has to be about 10 times larger than I and the time constant of the circuit l4l 5 some times smaller than the frequency of the relaxation oscillations.

11 claim:

1. In a television receiver for the reception of a transmission scanned at an even number of interlaced lines including a relaxation oscillation device consisting of a gas-filled discharge tube having a hot cathode, a grid and an anode, a lead to conduct to said grid the igniting synchronizing signals, a charging resistance in series and a storage condenser in parallel to said tube and means to connect the terminals of said condenser to the deflecting plates of a cathode ray tube: a timing circuit consisting of a second condenser and an impedance both in parallel to each other, one terminal of said timing circuit being connected to said cathode and the other to said storage condenser.

2. In a relaxation device according to claim 1, the second condenser having a capacity in the order of 10 times greater than that of the first condenser.

3. In a relaxation device according to claim 1, the time constant of the timing circuit being a few times smaller than the period of the relaxation oscillations.

KURT SCI-ILESINGER. 

